Hunger on the Wing (Part 1 of 3)

An African sky filled with locusts

Here’s another story from The Book of Deadly Animals. In the book, I didn’t have room for the whole story, since there were
more than 900 other animals to talk about. This longer version first appeared
in Discover.

*

One summer in the Oklahoma panhandle the grasshoppers were
everywhere. Every patch of weeds along the alley would erupt like a pan of
popping corn if I set foot in it. When we drove the highway, we inadvertently slaughtered
dozens. The collisions speckled our windshield with hemolymph. Their wings,
coffee-colored fans striped with yellow at the outer edges, lodged in our
wipers and fluttered in the onrushing air. Sometimes an entire grasshopper, or
most of one, would lodge there as well, struggling to get free as the wind tore
it to tatters.

They could be found in unaccustomed places that summer. For
several mornings running I saw two or three swimming in the dog's water dish.
The rosebushes took on the riddled look of lace, as though the grasshoppers had
tasted the leaves and found them unappealing but serviceable. In the country,
the cedar posts of barbed wire fences would seem at a glance to be shimmering
with heat, like a water mirage on the highway, but a second glance would show
the effect was not an optical illusion. The posts were simply crawling with
grasshoppers moving up or down for no apparent reason. They seemed to be moving
with great caution, edging past each other. When a stationary grasshopper got bumped,
it would draw its legs in tighter and shift its footing, like a person
uncomfortable on a crowded bus.

Then there was the jackrabbit. We found it beside a dirt
road on the way to the mailbox. It was dead, probably road-killed. Grasshoppers
were thick in the weeds and grass along that road, and dozens clustered on the
carcass. When someone poked at it experimentally, a few of the hoppers jumped
off and opened their wings and were carried away by the wind. Others crawled
off sluggishly. Some stayed put. With the carcass now more exposed, we could
see that it was bald in patches, and that its hide was wounded in shallow
divots, as if it had been hit all over with buckshot that failed to penetrate.
It seemed that the grasshoppers had been eating it.

As the season wore on, the grasshoppers grew absurdly thick.
Among the metallic green ones there were others, some yellow and spotted,
others a brighter green. All these I was familiar with, though I had never made
any particular study of them. But I began to see things utterly new to me. One
grasshopper was black and flecked with gray, like burned charcoal. Another was
black but flecked with a Tabasco red. This variety has been explained to me
thus: In outbreaks, grasshoppers are so plentiful that they overwhelm their
usual predators, offering them more food than they can use. Other grasshopper
species, rare enough to go unnoticed most of the time, get relief from
predators in this circumstance, and therefore are more likely to be around for
people to notice.

Other things seemed different too—there were a great many
large grasshoppers, thick as a lipstick. One morning on my driveway I found the
largest specimen I had ever seen, a yellowish creature longer than a soda can.
It was dead—a fact that gave me some comfort. Streams of black ants led up to
its carcass. Their presence was the first thing that convinced me I was seeing
a once-living creature rather than a toy. I turned it belly-up with a stick.
Its head and thorax were intact, but its abdomen was riddled with holes. I had
not seen this damage at first because its long wings concealed it from above.
Through the holes I glimpsed ants working at the grasshopper's half-hollow
hull.

What I've been describing is an infestation, a localized
population suddenly grown orders of magnitude beyond its usual numbers. The
causes are not thoroughly understood. In the United States, hot, dry weather
has something to do with it—the heat lets grasshoppers grow faster, and the
dryness discourages the fungi that would otherwise check the population's
growth.

Swarms of locusts—giant flying species of grasshoppers—are a
traveling variation on this phenomenon. They dominate a wide swath of this planet
almost every year. Moving in groups of millions, the locusts migrate over great
stretches of territory, settling down periodically to eat every bit of
vegetable matter in sight. They are hunger on the wing.

In the United States migratory swarms of locusts are
presumed to be a thing of the past. But a locust is really just an oversize
grasshopper in a gregarious mood. When grasshoppers of certain species gather
in great numbers, they begin to change their behavior. Normally, they are
somewhat solitary. If forced together they seem uncomfortable, leaping away
from each other. But hunger often forces them together when a bumper crop of
grasshoppers encounters a meager supply of food and they must compete for it.
If the crowding persists, the younger insects begin to change. The changes vary
with the species, but in general their bodies grow to massive size. Their wings
become clear and strong. Their colors shift dramatically—for example, from
green and yellow to solid black. Their proportions alter, their shape
essentially changing to accommodate flight. So profound is this change that scientists
in the past have mislabeled the two phases, solitary and gregarious, as
distinct species.

The creatures behave differently, too. They eat with
shocking voracity. They whirl into the air in groups, forming swarm clouds. The
swarms fly long distances, disrupting ecosystems for hundreds of miles. In the
1870s, one swarm was tracked from Montana to Texas, a distance of 1,500 miles.
Polluted layers of glaciers high in the Rockies show that their flight
sometimes takes them to altitudes beyond the normal range of grasshoppers. In
1874 a Nebraska doctor used telegraphs to find the far edges of a swarm he
observed flying overhead, establishing that its area exceeded that of Colorado.
Factoring in their rate and the depth of the swarm cloud, he arrived at an
estimate of 12.5 trillion grasshoppers. The Guinness Book of World Records lists
this swarm as the "Greatest Concentration of Animals" yet observed.
More rigorous methods were used on a swarm in Kenya in 1954, yielding the
figure of 10 billion grasshoppers in a swarm, which happened to be only one of
50 swarms in that country at the time.